Trust has been widely investigated both theoretically and empirically. Whether thought of as the result of a calculation of costs/benefits, a shared identity, or a leap of faith, there always seems to be an ‘as if’ rhetorical gesture which is ultimately needed to explain how actors move from the base of trust to expectations of trust via suspending judgment on uncertainty and fear of vulnerability to betrayal and exploitation — the actors ultimately act ‘as if’ they do not fear uncertainty (...) and vulnerability to betrayal. Yet this ‘as if’ element has remained seriously under-theorised. Drawing on Derrida's deconstruction, I propose a way of thinking this ‘as if’ element of trust. I thus argue that the decision to trust occurs in a terrain of structural undecidability. The latter is thought of as the possibility condition of trust as well as the subject of trust and a sense of responsibility for this trust. The aporiatic nature of undecidability makes this trust an auto-immune trust which obeys the tripartite logic of ‘without’ which both negates and affirms trust. (shrink)